Switchgrass and River Oats
In Autumn grasses take a more prominent place in the garden. In our garden, there are two grasses that do really well: Sea Oats (Chasmanthium latifolium) and Switchgrass (Panicum virgatum). There are also sedges (Carex sp.) that do well, but that’s a different story.
In my opinion River Oats have the most dramatic seedheads of all the ornamental grasses, especially when backlit by the sun. Another good thing about River Oats is that it will grow in sun or shade.
The downside of this grass is that it pops up all over the place, and the seedlings are tenacious little buggers. I try to cut down about half the seeds before they shatter, but even so I am pulling up trespassing River Oats all through the summer. Despite the nuisance factor, I’m not tempted to dig up our River Oats, because they just look really good.
River Oats are also called Northern Sea Oats, which is a mystery because they don’t grow by the sea. They do grow near woodland streams, though they’ll grow in our garden without needing a lot of moisture. The seedheads bear a slight resemblance to real oats, but the two plants are not in the same genus.
Switchgrass has a very different character. The panicles of tiny flowers have an ethereal, cloud-like quality. While River Oats have an arching habit, the stems and leaves of Switchgrass tend to be stiffly upright. It’s a big grass, about 6 feet tall (2 to 3 feet taller than River Oats), and is prominent in tall-grass prairies.
The roots of Switchgrass grow up to 30 feet deep, and they constitute an enormous mass. Scientists have estimated that an acre of Switchgrass contains 4 tons of underground roots. As a result, Switchgrass is considered to have great potential for carbon sequestration. If you want your garden to contribute to mitigating climate change, plant some Switchgrass.
Here’s a close up. Switchgrass will tolerate a bit of shade, but prefers full sun. It can adapt to moist or moderately dry soils. While it gradually forms big clumps, it does not run or self-sow, at least not in our garden.
Switchgrass does a decent job of catching the light. It can be a tricky grass to photograph, though.
We have both the straight species Switchgrass and the popular cultivar ‘Shenandoah’, which grows to 3-4 feet. I just planted a couple more ‘Shenandoah’ in the Lamppost Bed and the Parkway Bed. They were wasting away at the local Home Depot, which had them on sale for almost nothing. They look happier now.
In addition to its compact size, ‘Shenandoah’ is popular for its red-tipped foliage. The whole plant is supposed to turn burgundy in fall, but that doesn’t happen with ours. The straight species does not tend to have much color, though it will turn the color of straw by early winter.
What are your favorite autumn grasses?